1. Technical Field
The present invention relates to an optical pickup, and more particularly, to a laser diode driver for driving laser light sources of a N-wavelength optical pickup capable of recording on and playing N types of optical discs by using N laser beams having mutually different wavelengths.
2. Related Art
The optical disc drive is operative to read or record information recorded on an optical disc (a CD, a CD-ROM, a CD-R/RW, a DVD-ROM, a DVD±R/RW, a Blu-ray disc, an HD-DVD, or the like). These types of optical disc drives include an optical pickup for irradiating a laser beam on the optical disc and detecting the reflected light therefrom in order to perform reading information from the optical disc or recording information on the optical disc.
On the other hand, as well known, there has been developed a DVD device in which an optical disc drive having a particular pickup is built in order to record on and play any one of a digital versatile disc (DVD) and a compact disc (CD). Such a particular optical pickup performs a recording and playing operation by individually using two kinds of laser beams which have a short wavelength laser light (a wavelength of 650 nm or so) for DVDs and a long wavelength laser light (a wavelength of 780 nm or so) for CDs, which is called “dual wavelength optical pickup”.
Generally, there has been provided one type of the dual wavelength optical pickups including a first laser diode for DVDs that emits short wavelength laser light (i.e., first laser light) for DVDs and a second laser diode for CDs that emits long wavelength laser light (i.e., second laser light) for CDs (for example, see Patent Document 1).
However, there has been a problem that size of the optical pickup is increased due to an increase in the number of parts when the first laser diode and the second laser diode are separately provided. In order to deal with such a problem, there has been developed and introduced a laser diode (hereinafter, it is refer to as “one-chip laser diode”) in which the first laser diode and the second laser diode are integrated into one part (chip) (for example, see Patent Document 2). Such a one-chip laser diode can be miniaturized. In the one-chip laser diode, a first luminous point emitting a first laser light and a second luminous point emitting a second laser light are apart from each other by a predetermined distance (for example, 100 μm), and thus the first laser beam and the second laser beam are emitted at a predetermined distance apart from each other.
Recently, there has been developed a DVD device in which an optical disc drive having a particular pickup is built in order to record on and play not only a DVD and a CD but also an HD-DVD (High Definition DVD). Such a particular optical pickup performs recording and playing operation by individually using three kinds of laser beams which include a medium wavelength laser beam (a wavelength of 650 nm or so) for DVDs, a long wavelength laser beam (a wavelength of 780 nm or so) for CDs, and a short wavelength laser beam (a wavelength of 410 nm or so) for HD-DVDs, which is called “triple wavelength optical pickup”.
In the triple wavelength optical pickups, the one-chip laser diode (two-wavelength one package laser diode) for CDs and DVDs, a blue laser diode for HD-DVDs, may be used respectively, as disclosed in the Patent Document 2. In addition, hereinafter the HD-DVD is also referred to as HD.
Generally, an optical pickup includes a laser light source for emitting a laser beam and an optical system for guiding the emitted laser beam to an optical disc and guiding the reflected light from the optical disc to a photo detector. The optical system includes an objective lens which is disposed so as to face the optical disc. The laser light source and the photo detector are mounted on an outer wall of an optical base, and the optical system except for the objective lens is mounted in the optical base. The optical system also includes a front monitor for monitoring intensity of the laser light emitted from the laser light source. The laser light source is driven by a laser diode driver (LDD). The laser diode driver drives the laser light source on the basis of the intensity of the laser light monitored by the front monitor.
Patent Document 1: JP-A-2003-173563
Patent Document 2: JP-A-11-149652
In the triple wavelength optical pickup as described above, the one-chip laser diode (i.e., two-wavelength one package laser diode) and the blue laser diode for HD-DVDs can be employed as the laser light sources. In this case, it is required that a first laser diode driver for driving the two-wavelength one package laser diode and a second laser diode driver for driving the blue laser diode are provided as the laser diode driver. In addition, it is also required that two systems including a first front monitor for monitoring intensity of laser light emitted from the two-wavelength one package laser diode and a second front monitor for monitoring intensity of laser light emitted from the blue laser diode are provided as the front monitor. Hence, in the known triple wavelength optical pickup, there is a disadvantage that the number of terminals of the triple wavelength optical pickup increases in accordance with an increase in the number of input/output terminals of the laser diode drivers for driving the laser light sources.
Generally, there is a disadvantage in the case of an optical pickup dealing with N (N is an integer which is two or more) wavelengths.